Generally, combi rolls include two or more roll rings, which are kept separated by intermediate spacer rings, the entire set of rings being kept fixed on the roll shaft by way of, on one hand, a fixed stop ring, e.g., a shoulder of the roll shaft and, on the other hand, a lock nut, which via an internal thread may be tightened on a male thread of the shaft. Furthermore, between the lock nut and the set of roll rings and spacer rings, respectively, springs as well as additional rings may be present.
In many cases, the roll rings are manufactured from a hard material, such as cemented carbide, while intermediate spacer rings are manufactured of a softer or more ductile material, preferably steel or cast iron. Considerable torque should be transmitted from the roll shaft to the roll rings. When the roll rings exclusively are made of cemented carbide, the transmission of torque usually takes place by an axial (cylindrical) train of forces from the lock nut to the fixed stop ring via the end contact surfaces between the individual rings. More precisely, the torque is transmitted from the individual ring to an adjacent ring by friction action in those interfaces where an end surface of a ring is pressed against a co-operating end surface of the adjacent ring. In order to manage this purpose throughout the train of forces, the individual interfaces or friction joints between the rings have to be powerful, i.e., be able to transmit torque without the rings slipping in relation to each other.
In previously known combi rolls (see, for instance, U.S. Pat. Nos. 5,735,788 and 6,685,611), the end surfaces of the individual interfaces are metallic in so far as the surfaces have been generated by machining, such as turning and/or grinding, of a metal blank that should form the individual ring. In other words, the end surfaces of a spacer ring of steel are steel surfaces, while the end surfaces of cemented carbide roll ring are a cemented carbide surfaces. Dependent on the surface finish and the nature of the different materials, the friction between such surfaces may become inferior, something that may lead to the rings slipping in relation to each other. Another shortcoming of previously known combi rolls is that the roll rings as well as the spacer rings are formed with end surfaces that extend radially all the way from the inside of the ring to the outside thereof, i.e., from the envelope surface of the roll shaft to the external cylinder surface of the individual ring. This design of the end surfaces results in transmission of torque in a zone situated approximately halfway between the inside and the outside of the spacer ring, i.e., relatively near the envelope surface of the roll shaft. Furthermore, the surface pressure in the interfaces between the end contact surfaces will be fairly low because the contact surfaces are comparatively large.